Test Driven Development (C#)

Plan-Do-Check-Act
0 Originally called Plan-Do-Study-Act
0 Created by Walter Shewhart at Bell Labs during the
1930s

Iterative & Incremental
Development
0 The X-15 program in the 1950s used IID

Test-First in the Swinging 60s
0 X-15 team members seeded Project Mercury
0 Time-boxed half-day iterations
0 Tests were written first
0 Reviews after each iteration
0 Top-down development with stubs

We were doing incremental development as early as 1957, in Los Angeles, under
the direction of Bernie Dimsdale [at IBM’s Service Bureau Corporation]. He was
a colleague of John von Neumann, so perhaps he learned it there, or assumed it
as totally natural. I do remember Herb Jacobs (primarily, though we all
participated) developing a large simulation for Motorola, where the technique
used was, as far as I can tell, indistinguishable from XP.

When much of the same team was reassembled in Washington, DC in 1958 to
develop Project Mercury, we had our own machine and the new Share Operating
System, whose symbolic modification and assembly allowed us to build the
system incrementally, which we did, with great success.

Project Mercury was the seed bed out of which grew the IBM Federal Systems
Division. Thus, that division started with a history and tradition of incremental
development.

All of us, as far as I can remember, thought waterfalling of a huge project was
rather stupid, or at least ignorant of the realities… I think what the waterfall
description did for us was make us realize that we were doing something
else, something unnamed except for “software development.”

Gerald M. Weinberg

Waterfall in the 1970s & 80s
0 Blame the DoD and the CMMI

Other stuff was happening
0 Object-orientation
0 Simula from the late 60s
0 Smalltalk in the 70s at Xerox PARC
0 Software distribution

Into the 1990s
0 UML evolves
0 www arrives

The Testing Game
0 Red:
0 “Write a failing test”
0 Green:
0 “Pass the failing test”
0 Refactor
0 “Clean the implementation”

Write a failing test
0 To know what test to write, you must:
0 Analyze your problem
0 Design your solution
0 Code intentionally
0 To dislike “Big Upfront Design” is not to dislike design

Agile Problem Analysis
0 System Metaphor
0 Arises from the Architectural Spike
0 A simple design with the defining quality of explaining the
system design without reference to documents
0 User Experience
0 Arises from the set of all user stories
0 Provides a canvas onto which individual stories can be
painted
0 User Story
0 Describes a specific user expectation
0 Provides the functional constraints of implementation

User Stories
0 A user story comprises one or more sentences in the
everyday or business language of the end user that
captures what the user wants to achieve

Agile Solutions
0 “Walk the solution”: for each user story
0 Understand how this fits into the user experience
0 Understand where the necessary functional
implementation goes in the architecture
0 Design the functional implementation

Goldilocks Design
0 Design only what you need
0 avoid YAGNI (You Ain’t Gonna Need It)
0 Reuse existing implementation
0 be DRY (Don’t Repeat Yourself)
0 Prefer sketched designs over definitive design
0 allow TDD to be part of your design process
0 Don’t experiment in code
0 use spikes where necessary

First Exercise
0 Brainstorm a realistic candidate application
0 Write a small set of user stories
0 Elaborate a user experience
0 Articulate a system metaphor
0 Time limit: one hour

Analysis & Design
0 There are a variety of approaches to functional
analysis and implementation design
0 The most commonly used are:
0 The UML
0 CRC Cards
0 Design Patterns
0 Linguistics & Semantics
0 Personas
0 Storyboards

UML
0 The UML (Unified Modeling Language)
0 It has the advantage that many developers have at least
some familiarity
0 It has the disadvantage of significant complexity
0 Most agile practitioners use ‘sketch’ UML, typically on a
whiteboard, in order to convey a mental model of a
proposed solution
0 Be indicative, not definitive

UML Use Case Diagram
0 Describes the functionality provided by a system in
terms of actors and their goals represented as use
cases

UML Activity Diagram
0 Used to describe the
business and operational
step-by-step workflows
of components in a
system

UML Sequence Diagram
0 Shows how processes operate with one another and
in what sequence

UML Class Diagram
0 Describes the structure of a system by showing the
system's classes, their attributes, methods, and the
relationships among the classes

CRC Cards
0 Class Responsibility Collaboration cards are a
brainstorming tool, proposed by Ward Cunningham and
Kent Beck
0 They are typically used when determining which classes
are needed and how they will interact
0 CRC cards are usually created from index cards on which
are written:
0 The class name
0 Any base or derived classes (if applicable)
0 The responsibilities of the class
0 The names of other classes with which the class will
collaborate to fulfil its responsibilities

Design Patterns
0 A general reusable solution to a commonly occurring
problem within a given context
0 A design pattern is not a finished design that can be
transformed directly into code; it is a description or
template for how to solve a problem that can be used
in many different situations
0 Typically show relationships and interactions
between classes or objects, without specifying the
final application classes or objects that are involved

Some Creational Patterns
0 Factory method
0 Define an interface for creating an object, but let derived classes decide
which class to instantiate
0 Lazy initialization
0 Tactic of delaying the creation of an object, the calculation of a value, or
some other expensive process until the first time it is needed
0 Object pool
0 Avoid expensive acquisition and release of resources by recycling objects
that are no longer in use
0 Resource acquisition is initialization
0 Ensure that resources are properly released by tying them to the lifespan
of suitable objects
0 Singleton
0 Ensure a class has only one instance, and provide a global point of access
to it

Some Structural Patterns
0 Adapter
0 Convert the interface of a class into another interface clients
expect
0 Bridge
0 Decouple an abstraction from its implementation allowing the
two to vary independently
0 Facade
0 Provide a unified interface to a set of interfaces in a subsystem
0 Proxy
0 Provide a surrogate or placeholder for another object to
control access to it

Some Behavioural Patterns
0 Chain of responsibility
0 Avoid coupling the sender of a request to its receiver by giving
more than one object a chance to handle the request
0 Command
0 Encapsulate a request as an object, thereby letting you
parameterize clients with different requests, queue or log
requests, and support undoable operations
0 Iterator
0 Provide a way to access the elements of an aggregate object
sequentially without exposing its underlying representation
0 Null object
0 Avoid null references by providing a default object

Linguistics & Semantics
0 Using the meanings and
relationships of words and
phrases employed in the user
stories and other material to
construct a language map of
the problem domain
0 Especially useful when
dealing with ‘expert’ systems

Personas
0 Fictional characters
created to represent
the different user
types within a
targeted
demographic, attitude
and/or behaviour set
that might use a
site, brand or product
in a similar way

Storyboards
0 A technique
borrowed
from the
film
industry
0 Shows the
user
experience
in sequence

Second Exercise
0 Take one or more of the user stories from the first
exercise and apply a selection of the analysis and
design techniques
0 Draw up a list of the strengths and weaknesses of the
techniques in relation to these particular user stories

Testing Frameworks
0 MSTest
0 Built-in to Visual Studio
0 Pex
0 Experimental white-box testing from MS Research
0 NUnit
0 Early open source port of JUnit for .net
0 MbUnit
0 Another open source framework
0 xUnit
0 Open source reset of NUnit
0 SpecFlow
0 Open source behaviour-driven-development framework

Arrange, Act, Assert
0 The default pattern for unit tests
1. Arrange all necessary preconditions and inputs
2. Act on the object or method under test
3. Assert that the expected results have occurred

Test naming conventions
0 Ad-hoc
0 Anything goes
0 Behavioural
0 Tests are named according to the behaviour under test
0 Good fit for collaboration tests (distinct from unit tests)
public void customer_pays_in_cheque_to_current_account()

0 Contractual
0 Names follow the unit contract under test
http://alandean.blogspot.com/2011/11/unit-test-naming-convention.html

xUnit Assertions
0 Fundamentals
0 Assert.True(…) or Assert.False(…)
0 Assert.Null(…) or Assert.NotNull(…)
0 Assert.Equal(…) or Assert.NotEqual(…)
0 Assert.Same(…) or Assert.NotSame(…)
0 Exceptions
0 Assert.Throws<T>(…) or Assert.DoesNotThrow(…)
0 Type checks
0 Assert.IsType(…) or Assert.IsNotType<T>(…)
0 Assert.IsAssignableFrom<T>(…)
0 IEnumerable
0 Assert.Empty(…) or Assert.NotEmpty(…)
0 Assert.Single(…)
0 Assert.Contains(…) or Assert.DoesNotContain(…)
0 Assert.InRange(…) or Assert.NotInRange(…)

System.Diagnostics.Debug
0 Assertions
0 Debug.Assert(…)
0 Debug.Fail(…)
0 Publication
0 Debug.Print(…)
0 Debug.Write(…) or Debug.WriteIf(…)
0 Debug.WriteLine(…) or Debug.WriteLineIf(…)

TDD at the Keyboard
1. Add a new test
2. Run all tests and see if the new one fails
3. Write some code
4. Run all tests and see them succeed
5. Refactor code
6. Repeat

Exercise 3
0 Create a solution with two class libraries:
0 TicTacToe
0 TicTacToe.Facts
0 Add a reference to xUnit.net in the Facts library
0 http://nuget.org/

0 Use TDD to implement Tic-Tac-Toe
0 http://gojko.net/2009/08/02/tdd-as-if-you-meant-it-revisited/

Refactoring Code
0 A disciplined technique for restructuring an existing body of code,
altering its internal structure without changing its external behaviour
0 Usually motivated by noticing a code smell
0 There are two general categories of benefits to the activity of refactoring
0 Maintainability
0 It is easier to fix bugs because the source code is easy to read and the
intent of its author is easy to grasp
0 This might be achieved by reducing large monolithic routines into a set of
individually concise, well-named, single-purpose methods
0 It might be achieved by moving a method to a more appropriate class, or
by removing misleading comments.
0 Extensibility
0 It is easier to extend the capabilities of the application if it uses
recognizable design patterns, and it provides some flexibility where none
before may have existed

Refactoring Techniques
0 Techniques that allow for more abstraction
0 Encapsulate Field: force code to access the field with getter and setter methods
0 Generalize Type: create more general types to allow for more code sharing
0 Replace Conditional with Polymorphism: move each leg of the conditional to an
overriding method in a derived class and make the original method abstract
0 Techniques for breaking code apart into more logical pieces
0 Extract Method: turn part of a larger method into a new method
0 Extract Class: moves part of the code from an existing class into a new class
0 Techniques for improving names and location of code
0 Move Method or Field: move to a more appropriate class
0 Rename Method or Field: changing the name to one that better reveals its purpose
0 Pull Up: move to a base class
0 Push Down: move to a derived class
0 Longer list
0 http://martinfowler.com/refactoring/catalog/index.html

Exercise 4
0 RomanNumerals
0 RomanNumerals.Facts
0 Use TDD to solve the problem
0 https://sites.google.com/site/tddproblems/all-problems-1/Roman-number-conversion

0 Refactor the code as you go

Test Doubles
0 Objects that mimic real objects for testing purposes
0 Dummies
0 Have no behaviour or throw exceptions
0 Stubs
0 Provide the behaviour of a real object
0 Spies
0 Record activity for later verification
0 Mocks
0 Define the expected activity before the test is run
0 Fakes
0 Employ a simpler implementation such as an in-memory database
0 See also
http://martinfowler.com/articles/mocksArentStubs.html

Mocking Frameworks
0 Visual Studio doesn’t have one built-in
0 Moles
0 Experimental framework from MS Research
0 Open source
0 Moq, NCrunch, NMock2, Rhino Mocks, fakeiteasy
0 Commercial
0 TypeMock Isolator, JustMock

SOLID Code
0 Single Responsibility principle
0 An object should have only a single responsibility
0 Open/Closed principle
0 Objects should be open for extension, but closed for modification
0 Liskov Substitution principle
0 Objects should be replaceable with instances of their derived
types without altering correctness
0 Interface Segregation principle
0 Many client specific interfaces are better than one general
purpose interface
0 Dependency Inversion principle
0 Depend upon abstractions; do not depend upon concretions

Inversion of Control
0 Microsoft
0 Unity
0 Common Service Locator
0 Open source
0 Castle Windsor, Autofac, StructureMap, Ninject, LinFu

Exercise 5
0 Translator
0 Translator.Facts
0 Use TDD to solve the problem
0 TODO

0 Refactor the code as you go
0 Use test doubles to isolate tests from dependencies
and resources to achieve SOLID code
0 Time limit: two hours

Test Driven Development (C#)

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